I've added a facebook 'like' button to my site using code generated by facebook, but when I check my page with an HTML validator it says that the code contains errors. I know virtually nothing about HTML; does such an error actually matter ( I read somewhere that search engines don't lke them)? If so, is what can I do about it?

There are two alternative codes: the XFBML code seems to contain 4 errors (here in red):
<script src="http://connect.facebook.net/en_US/all.js#xfbml=1"></script><fb:like href="http://www.richardwhincop.co.uk/welcome.html" font="arial"></fb:like>

The iframe code contains one error (again, in red):
<iframe src="http://www.facebook.com/plugins/like.php?href=http%3A%2F%2Fwww.richardwhincop.co.u k%2Fwelcome.html&amp;layout=standard&amp;show_face s=true&amp;width=450&amp;action=like&amp;font=aria l&amp;colorscheme=light&amp;height=80" scrolling="no" frameborder="0" style="border:none; overflow:hidden; width:450px; height:80px;" allowTransparency="true"></iframe>

Any advice much appreciated.